1. Field of the Invention
The present invention relates to a solid electrolytic capacitor.
2. Description of the Related Art
A solid electrolytic capacitor is a capacitor in which an oxide film (dielectric) is formed on a surface of a valve metal such as aluminum by anodization, and a solid electrolytic layer is in contact with the oxide film. In the solid electrolytic capacitor, the valve metal constitutes an anode, and the solid electrolytic layer constitutes a cathode.
FIG. 7 is a cross-sectional view showing the structure of a conventional solid electrolytic capacitor of a type in which current is collected at end faces thereof (hereinafter, this type is referred to as xe2x80x9cend face-current collecting type solid electrolytic capacitor). A solid electrolytic capacitor 1 of FIG. 7 includes a laminate of a plurality of capacitor elements 2, and the laminate is coated with an encapsulating resin 3. The capacitor element 2 includes an anode 2a, and a dielectric layer 2b, a solid electrolytic layer 2c, and a conductive layer 2d that are laminated on the surface of the anode 2a in this order. The conductive layer 2d is connected to a lead 5 via a conductive adhesive 4. A part of the lead 5 is exposed from the encapsulating resin 3, and the lead 5 is connected to a cathode terminal 6 via the conductive adhesive 4 at the exposed portion. Similarly, a part of the anode 2a is exposed from the encapsulating resin 3, and the anode 2a is connected to an anode terminal 7 via the conductive adhesive 4 at the exposed portion.
However, in the conventional end face-current collecting type solid electrolytic capacitor 1, a connection resistance in the portion where the anode 2a, the conductive resin 4 and the anode terminal 7 are connected is large, and a connection resistance in the portion where the lead 5, the conductive resin 4 and the cathode terminal 6 are connected is large, and therefore the equivalent series resistance (ESR) of the capacitor is large. In order to reduce the connection resistance, a plating process technique that allows connection at a low resistance or a conductive adhesive that allows connection at a low resistance should be developed.
However, since the connection resistance is inversely proportional to the area of the connection surface, sufficient effects cannot be obtained simply by applying a plating process technique or a conductive adhesive that allows connection at a low resistance to a flat connection surface.
Therefore, with the foregoing in mind, it is an object of the present invention to provide a solid electrolytic capacitor having a low ESR.
A first solid electrolytic capacitor of the present invention includes a capacitor element including a capacitance forming portion; an encapsulating resin with which the capacitance forming portion is coated; an anode terminal and a cathode terminal that are provided such that at least a part thereof is outside the encapsulating resin; and a lead. The capacitor element includes an anode, and a dielectric layer and a solid electrolytic layer that are laminated on a portion of the anode in this order. The lead is electrically connected to the solid electrolytic layer. The surface of at least one component selected from the anode and the lead has roughness in at least one connection portion selected from a connection portion between the anode and the anode terminal and a connection portion between the lead and the cathode terminal.
In this specification, xe2x80x9cbeing electrically connectedxe2x80x9d means that two components are connected directly or connected via a component serving as an electrical connection.
A second solid electrolytic capacitor of the present invention includes a capacitor element including a capacitance forming portion; an encapsulating resin with which the capacitance forming portion of the capacitor element is coated; an anode terminal and a cathode terminal that are provided such that at least a part thereof is outside the encapsulating resin; and a lead. The capacitor element includes an anode, and a dielectric layer and a solid electrolytic layer that are laminated on a portion of the anode in this order. The lead is electrically connected to the solid electrolytic layer. At least one component selected from the anode and the lead is electrically connected to at least one terminal selected from the anode terminal and the cathode terminal via a conductor provided on a surface of the component that is parallel to a direction in which the component is drawn out.
In the first solid electrolytic capacitor of the present invention, the surface of the anode or the cathode lead in the connection portion with the electrode terminal is processed so as to increase the surface area. Therefore, the first solid electrolytic capacitor has a small ESR.
In the second solid electrolytic capacitor of the present invention, a conductor is provided on the surface of the anode drawn-out portion or the cathode lead, and the anode drawn-out portion or the cathode lead is connected to the electrode terminal via the conductor. Therefore, the second solid electrolytic capacitor has a current collecting path having a large cross-section area and a small ESR.